Quartz glass having excellent resistance against plasma corrosion and method for producing the same

ABSTRACT

As a jig material to use under plasma reaction for producing semiconductors the present invention provides a quartz glass having resistance against plasma corrosion, particularly corrosion resistance against fluorine-based plasma gases, and which is usable without causing anomalies to silicon wafers; the present invention furthermore provides a quartz glass jig, and a method for producing the same. A quartz glass containing 0.1 to 20 wt % in total of two or more types of metallic elements, said metallic elements comprising at least one type of metallic element selected from Group 3B of the periodic table as a first metallic element and at least one type of metallic element selected from the group consisting of Mg, Ca, Sr, Ba, Sc, Y, Ti, Zr, Hf, lanthanoids, and actinoids as a second metallic element, provided that the maximum concentration of each of the second metallic elements is 1.0 wt % or less.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to quartz glass and a quartz glass jig foruse in producing a semiconductor and having excellent plasma corrosionresistance, and to a method for producing any one of the quartz glassand the quartz glass jig.

2. Description of the Related Art

In such production of the semiconductor, for example, in the productionof a semiconductor wafer, in accordance with a recent trend inincreasing a diameter thereof, an improvement of processing efficiencyis performed by using a plasma reaction apparatus in an etching processand the like. For example, in a process of etching the semiconductorwafer, an etching treatment is performed by using a plasma gas such as afluorine (F)-based plasma gas.

However, when conventional quartz glass is placed, for example, in anF-based plasma gas atmosphere, SiO₂ and the F-based plasma gas areallowed to react with each other on a surface of the quartz glass, tothereby generate SiF₄. Since a boiling point of the thus-generated SiF₄is −86° C., it is easily sublimated and, then, the quartz glass iscorroded to a great extent causing a reduction in thickness orroughening the surface thereof. Thus, the quartz glass was found to beunsuitable for use as a jig in an atmosphere of the F-based plasma gas.

As described above, in the conventional quartz glass, a serious problemwas generated in corrosion resistance, namely, plasma corrosionresistance, in a plasma reaction at the time of producing thesemiconductor, particularly, an etching treatment using the F-basedplasma gas. Under these circumstances, proposals in which aluminum or analuminum compound covers a surface of a quartz glass member to improvethe plasma corrosion resistance (refer to JP1997-95771A, JP1997-95772Aand JP1998-139480A) or another proposal for plasma corrosion resistantglass in which aluminum is allowed to be contained in quartz glass toimprove the plasma corrosion resistance (JP1999-228172A) have been made.

According to the present technique, quartz glass was prepared byheat-fusing a quartz glass powder mixed with 5 wt % of alumina powder invacuum. The plasma corrosion resistance of the thus-prepared quartzglass was investigated. As a result, an etching rate thereof was reducedby 40% to 50% compared with a quartz glass member without containing anydopant at all.

As a reason for that, it is assumed that a boiling point of AlF₃ that isgenerated on the reaction with the F-based plasma gas is 1290° C. thatis far higher than that of SiF₄. Therefore it is considered that, whilea SiF₄ portion is corroded to a great extent, sublimation on a surfaceof an AlF₃ portion occurs to a small extent and, accordingly, adifference in an etched quantity becomes large therebetween.

In a same way of thinking, quartz glass containing 0.1 to 20 wt % of atotal of two types or more of metallic elements which comprises a firstmetallic element that is a type belonging to 3B of the periodic tableand a second metallic element that is at least one type selected fromthe group consisting of Zr, Y, lanthanoids and actinoids is alsoproposed (JP2002-220257A).

The first and second metallic elements contained in the above-describedquartz glass each have a higher boiling point in a fluoride form thereofthan that of Si, to thereby reduce an etching rate. For example, since aboiling point of NdF₃ is 2327° C., when the plasma corrosion resistanceis investigated, the etching rate thereof has reduced by 50% to 70% ascompared with that of the quartz glass member without containing anydopant at all.

SUMMARY OF THE INVENTION

Although the above described technique can obtain a remarkable effect inimprovement of the plasma corrosion resistance, such second metallicelements which have been doped are released with the progress of etchingand, then, a portion thereof is adhered on a silicon wafer and the like,to thereby become a factor of a defect.

In order to solve the above-described problems, the present inventorshave exerted an intensive study and, as a result, found quartz glasshaving 0.1 to 20 wt % of a total of the first and second metallicelements, in which, by allowing a maximum concentration of each of thesecond metallic elements to be 2.0 wt % or less, preferably 1.0 wt % orless, an excellent corrosion resistance is imparted, a concentration ofthe second metallic elements to be released in an atmosphere isdecreased with the progress of the etching in an etching process and,even when the thus-released second metallic element is adhered on thesilicon wafer, it is at a level of a detection limit or lower.

Namely, the quartz glass being excellent in plasma corrosion resistanceaccording to the present invention, which is quartz glass containing 0.1to 20 wt % of a total of two types or more of metallic elements, ischaracterized in that the metallic elements comprise a first metallicelement which is at least one type selected from 3B group of theperiodic table and a second metallic element which is at least one typeselected from the group consisting of Mg, Ca, Sr, Ba, Sc, Y, Ti, Zr, Hf.lanthanoids and actinoids in which a maximum concentration of each ofsuch second metallic elements is 2.0 wt % or less and, preferably, 1.0wt % or less.

It is preferable that two types or more of the above-described secondmetallic elements are contained. Further, it is favorable that a totalof the second metallic elements are 2.0 wt % or more and, preferably,1.0 wt % or more.

It is preferable that the above-described first metallic element is Aland the above-described second metallic element contains at least onetype selected from the group consisting of Y, La, Ce, Nd, Sm and Gd.

It is favorable that a blending ratio between the above-described firstmetallic element (M1) and one type or a total of two types or more ofthe second metallic elements (M2) is in a relation of (M1)/(M2)=0.1 to20 in terms of an atomic number ratio.

It is preferable that, in the quartz glass according to the presentinvention, contents of bubbles and foreign matters are less than 100 mm²in terms of a projected area per 100 cm³.

A quartz glass jig according to the present invention is characterizedin that a metallic element-containing layer comprising quartz glassaccording to the present invention is formed in a thickness of up to atleast 1 mm from a surface thereof.

A first aspect of a method for producing the quartz glass according tothe present invention, which is a method for producing quartz glassexcellent in plasma corrosion resistance from quartz powder by aVerneuil method using a furnace comprising a burner which supplies rawmaterial powder and a gas, and a rotatable platform, is characterized inthat, at the time a quartz glass ingot is prepared by supplying the rawmaterial powder prepared by blending quartz powder with powder of theabove-described first and second metallic elements or powder ofcompounds thereof into the burner and, then, heating, fusing it and,thereafter, dropping the resultant article on the platform, atemperature of a surface of the quartz glass ingot is raised to 1800° C.or higher.

On this occasion, as the platform, a platform comprising, as a rawmaterial, any one of quartz glass doped with a metallic element,graphite, alumina ceramics, zirconia ceramics, ceramics containingalumina and zirconia, and other ceramics, or another platform preparedby combining any one of these raw materials and quartz glass isfavorably used.

As for an upper ceiling of the above-described furnace, long sheets eachhaving a strip shape and using any one of alumina ceramics and otherceramics, as a raw material, are aligned and, then, used or a SUS sheetcooled by water is favorably used.

It is also favorable that an electric heater is disposed on a sidewallof the furnace and, then, a side face in a heating area is allowed to becontrollably heated by the electric heater.

It is also favorable that, in the Verneuil method using an oxyhydrogenflame, the burner having a structure in which the oxyhydrogen flameforms a focus is used.

It is also favorable that an atmosphere in the heating area in thefurnace is in a reducing state containing hydrogen.

In the case of the Verneuil method using the oxyhydrogen flame, it isfavorable that a ratio of hydrogen/oxygen to be supplied to a heatingatmosphere area in the furnace is 2.5 or more. Even in the case of theVerneuil method using arc plasma, same effect as in the above can beobtained.

A second aspect of the method for producing the quartz glass accordingto the present invention is characterized in that a solution prepared bydissolving the above-described first and second metallic elements,oxides thereof or compounds thereof and the quartz powder, while mixingwith one another, in pure water, an acidic solution, an alkalinesolution, or an organic solvent is dried to prepare a formed body and,then, the thus-prepared formed body is heat-fused at 1300° C. or higherin a non-acidic atmosphere and, accordingly, an ingot is prepared.

A third aspect of the method for producing the quartz glass according tothe present invention is characterized in that powder prepared by mixingthe above described first and second metallic elements, oxides thereofor compounds thereof with quartz powder is packed in a quartz tube and,then, heat-fused at 1300° C. or higher from an outside face of the tubewhile allowing an inside of the tube to be in a reduced pressure bysucking the air therein, to thereby prepare an ingot.

A fourth aspect of the method for producing the quartz glass accordingto the present invention is characterized in that a volatile compoundgas of the above described first and second metallic elements isdiffused in a quartz soot having a hydroxyl group and, then, aftersubjected to a heating treatment in the temperature range of from 200°C. to 1100° C., heat-fused at 1300° C. or higher in a non-acidicatmosphere, to thereby prepare an ingot.

A fifth aspect of the method for producing the quartz glass according tothe present invention is characterized in that a quartz soot is dippedin a solution prepared by mix-dissolving the above described first andsecond metallic elements or compounds thereof which are dissolvable inpure water, an acidic solution, an alkaline solution, or an organicsolvent, in the pure water, the acidic solution, the alkaline solution,or the organic solvent, dried and, then, heat-fused at a temperature of1300° C. or higher in a non-acidic atmosphere.

In the first to fifth aspects of the method for producing the quartzglass according to the present invention, it is preferable that thethus-prepared quartz glass ingot is heat-formed at a temperature of1300° C. or higher under a pressure of 2 kg/cm² or higher in an inertgas atmosphere.

A method for preparing a quartz glass jig according to the presentinvention is characterized in that a solution prepared by mix-dissolvingany of the first and second metallic elements, oxides thereof orcompounds thereof which are dissolvable in pure water, an acidicsolution, an alkaline solution, or an organic solvent, in the purewater, the acidic solution, the alkaline solution, or the organicsolvent is coated on a surface of a previously prepared quartz glass jigand, then, the thus-coated surface is heat-fused.

In the method for producing the quartz glass jig according to thepresent invention, it is preferable that the thus-produced quartz glassjig is heat-formed at a temperature of 1300° C. or higher under apressure of 2 kg/cm² or higher in an inert gas atmosphere.

The quartz glass and the quartz glass jig according to the presentinvention are, as a jig material for plasma reaction for use inproduction of a semiconductor, excellent in plasma corrosion resistance,particularly, the corrosion resistance against an F-based plasma gas andhave an effect such that they can be used without causing any abnormalfeature on a silicon wafer. Further, the method according to the presentinvention has an advantage in that the quartz glass and the quartz glassjig excellent in the plasma corrosion resistance can efficiently beproduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic explanation view showing an example of anapparatus employed in a method of producing a quartz glass according tothe invention.

FIG. 2 is a schematic perspective view showing an example of an upperceiling of a furnace.

FIG. 3 is a top view showing another example of an upper ceiling of afurnace.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments according to the present invention will bedescribed with reference to the accompanying drawings; however, they arerepresentative and shown only for illustrative purposes and it goeswithout saying that various modifications and alterations can be madewithout departing from the scope of the general inventive concept of thepresent invention.

Quartz glass according to the present invention, which is quartz glasscontaining 0.1 to 20 wt % of a total of two types or more of metallicelements, is characterized in that the metallic elements comprise afirst metallic element which is at least one type selected from 3B groupof the periodic table and a second metallic element which is at leastone type selected from the group consisting of Mg, Ca, Sr, Ba, Sc, Y,Ti, Zr, Hf, lanthanoids and actinoids in which a maximum concentrationof each of such second metallic elements is 2.0 wt % or less and,preferably, 1.0 wt % or less.

Although an entire concentration of the above-described metallicelements to be contained is 0.1 to 20 wt %, when it is less than 0.1 wt%, there is no improvement of etching resistance, while, when it is morethan 20 wt %, bubbles are generated to a great extent and, accordingly,the quartz glass can no more be used as a glass body. From thestandpoint of the improvement of corrosion resistance, the entireconcentration of the metallic elements to be contained is preferably 1to 20 wt % and, more preferably, 2 to 20 wt %.

When Al which is the first metallic element is contained together withthe second metallic element, Al is incorporated in a quartz network tocause a negative charge and, then, the thus-caused negative charge andthe second metallic element which holds a positive charge attract witheach other to alleviate charges therebetween and, as a result, metallicelements are suppressed from being solidified as oxides thereof. As forthe first metallic elements which each tend to have a negative charge ina same manner as in Al, a metallic element belonging to 3B of theperiodic table can be selected; however, since Al is an element whichhas no problem in a production process of a semiconductor, Al is mostsuitable as the first metallic element. Further, as for the secondmetallic elements, since Y, La, Ce, Nd, Sm and Gd are high in theabove-described effect, easily handled, at low cost and easily availablein the market, they are favorable.

It is preferable that a blending ratio between the above-described firstmetallic element (M1) and one type or a total of two types or more ofthe second metallic elements (M2) is in a relation of (M1)/(M2)=0.1 to20 in terms of atomic number ratio. When this ratio is less than 0.1,the above-described effect of alleviation cannot be obtained andturbidity is generated, while, when it is more than 20, charge stabilityis collapsed, to thereby generate bubbles and foreign matters in atransparent glass body to a great extent.

When the glass body produced while satisfying above-described conditionsis used in a dry-etching process, an etched substance is scattered in agaseous state in an etching chamber and, then, a portion of the etchedsubstance is adhered on an Si wafer; therefore, a gas cleaning of theetching chamber and a liquid cleaning of the Si wafer are periodicallyperformed every about 100 hours. On this occasion, when the secondmetallic element on the Si wafer is equal to or less than the detectionlimit, there causes no problem in a succeeding production process of asemiconductor device. As a result of a study executed by the presentinventors, it has been found that, when the quartz jig placed in theetching chamber was doped with more than 2.0 wt % of each of the secondmetallic elements, although etching corrosion resistance was improved, alarge -amount of second metal impurities were, after being scattered,deposited on the Si wafer and was detected even after the Si wafer wassubjected to cleaning, while, when it was doped with 2.0 wt % or lessthereof, the second metal impurities were no more detected on the Siwafter, after the Si wafer was subjected to cleaning. Measurements wereperformed by a fluorescent X ray.

Namely, by allowing a maximum concentration of each of the secondmetallic elements to be 2.0 wt % or less and, preferably, 1.0 wt % orless, a concentration of the second metallic elements to be released inthe atmosphere with the progress of etching is reduced and, then, evenwhen they are adhered on the silicon wafer, the concentration thereofbecomes at a level of the detection limit or lower.

However, when a stronger etching corrosion resistance is required, sincethe etching corrosion resistance and a concentration of a doped metalare in a proportional relation with each other, a doping concentrationof 2.0 wt % or more becomes necessary. In order to solve both theproblem of metallic element detection on the Si wafer and the etchingcorrosion resistance, the second metallic elements are allowed to be 2types or more and, while restricting a concentration of each of them tobe 2.0 wt % or less and, preferably, 1.0 wt % or less, a concentrationof an entire amount thereof is allowed to be 2.0 wt % or more and,preferably, 1.0 wt % or more and, as a result, it has become possible toassure non-detection of each of the metallic elements and a sufficienteffect of the etching corrosion resistance.

When a doped quartz material as having such excellent etching corrosionresistance as described above is used as a quartz jig, an entire body ofthe jig is not necessarily made of the doped quartz material. By forminga metallic element-containing layer which contains 0.1 to 20 wt % of theabove-described metallic elements in a thickness of up to at least 1 mmfrom the surface thereof, a portion of the doped quartz material ispresent on the surface of the jig at least in an actual productionprocess of etching.

A first aspect of a production method according to the present inventionis a method for producing quartz glass excellent in plasma corrosionresistance from quartz powder by the Verneuil method. The first aspectof the method according to the present invention will be described belowwith reference to FIGS. 1 to 3. FIG. 1 is a schematic explanatorydiagram showing an example of an apparatus by the Verneuil method to beused in a method for producing quartz glass according to the presentinvention. FIG. 2 is a schematic perspective explanatory diagram showingan example of an upper ceiling of a furnace. FIG. 3 is a top view ofanother example of the upper ceiling of the furnace.

In FIG. 1, 10 denotes a furnace which comprises an upper ceiling 14 onwhich a burner 12 that supplies raw material powder and a gas isdisposed, a sidewall 16 and a rotatable platform 18. Raw material powderwhich is mixed powder of powder of the above-described first and secondmetallic elements or compounds thereof and quartz power is supplied tothe burner 12 and, then, heat-fused and dropped on the rotating platform18, to thereby prepare a quartz glass ingot 22. On this occasion, byraising a temperature of a surface of the quarts glass ingot 22 to 1800°C. or higher, the quartz powder is sufficiently fuse-liquefied and themetallic element powder can sufficiently be diffused in thethus-fuse-liquefied quartz powder. Further, In FIG. 1, an exhaust port13 is disposed in an upper portion of the furnace; however, a positionof the exhaust port is not particularly limited according to the presentinvention and the exhaust port may be disposed in a sidewall or a lowerportion of the furnace. Still further, a shape or the like of thefurnace is not particularly limited and a known furnace to be used inthe Verneuil method can widely be used.

As for the platform 18 on which the quartz powder mixed with themetallic elements is dropped, it is favorable that a platform whichuses, as a raw material, any one of quartz glass doped with a metallicelement, graphite, alumina ceramics, zirconia ceramics, ceramicscontaining alumina or zirconia and other ceramics than theabove-described ceramics is used or another platform which is preparedby using any one of these raw materials and quartz glass in combinationsis used. This is because, since the platform 18 is severely heated for along time and tends to be deformed or broken, it is indispensable thatthe platform 18 is excellent in heat resistance and strength.

FIG. 2 is a perspective schematic explanatory diagram showing an exampleof an upper ceiling 14 disposed in an upper portion of a heating area20. In FIG. 2, the upper ceiling 14 a is formed by aligning a pluralityof long sheets 15 each having a strip shape in parallel. FIG. 3 is a topview of another example of the upper ceiling 14. In FIG. 3, the upperceiling 14 b, which is made of a stainless steel sheet (SUS sheet)provided with a baffle plate 17 inside, is cooled by allowing water tobe flowed in from a water inlet 21, flowed along a water channel 19 and,then, discharged from a water outlet 23.

As for the upper ceiling 14 of the heating area 20, it is favorablethat, as shown in FIG. 2, long sheets each having a strip shape in whichalumina ceramics or other ceramics than the alumina ceramics are used asraw materials are used after being aligned or, as shown in FIG. 3, theSUS sheet cooled by water is used. The upper ceiling portion tends to bebroken in a same manner as in the platform and, even when such breakageis minute, a foreign matter caused by the breakage is scattered anddropped on the ingot 22, to thereby cause a bubble. In order to preventthe bubble from being generated, it is necessary to allow not only theraw material itself but also the shape thereof to be such material andshape which are hard to cause the minute breakage and, the long sheethaving a strip shape is effective. Further, when the SUS sheet cooled bywater is used, the minute breakage is not generated at all and,therefore, it is extremely effective means.

As shown in FIG. 1, it is also favorable that an electric heater 24 isdisposed on the sidewall 16 and, then, a side face of the heating area20 is allowed to be controllably heated by the electric heater 24. Thisis because, in a process of preparing the quartz ingot 22, by heatingthe side face, an oxyhydrogen flame to be used can be small in quantityand, then, heat loads to the furnace upper ceiling 14, the sidewall 16and the platform 18 can be reduced, to thereby remarkably stabilize aproduction state. Further, after the quartz ingot 22 is prepared, whenthe oxyhydrogen flame is extinguished, a temperature of the heating areais sharply decreased, and the quartz glass is also quenched anddistorted, to thereby generate a crack inside the glass body. For thisaccount, it is extremely effective in preventing the crack from beinggenerated that, after such extinguishment, the side face of the furnaceis heated by the electric heater to allow the quartz glass to begradually cooled.

In the Verneuil method using the oxyhydrogen flame, it is also favorableto use the burner having a structure in which the oxyhydrogen flameforms a focus. This is because a burning energy of an oxyhydrogen gascan be concentrated and, then, mixed powder of the metallic elements andquartz glass powder to be dropped can be exposed to such concentratedburning energy and, for this account, a heating effect becomes extremelylarge.

It is favorable that an atmosphere of the heating area 20 is in areducing state containing hydrogen. This is because, when the metallicelement is the oxide thereof, a reductive reaction of the oxide isprogressed and, then, the metallic element becomes easily fused in thequartz glass. Further, remaining oxygen that causes bubble formation ischanged into H₂O and, then, removed.

In the above-described Verneuil method, when the oxyhydrogen flame isused as a heating source, by allowing a ratio of hydrogen/oxygen to besupplied from the burner 12 into a heating atmosphere area 20 to be 2.5or more, the reductive reaction of the oxide is progressed and, then,the metallic element becomes easily fused in the quartz glass. When theVerneuil method is used, arc plasma may be used as the heating source.Even with such arc heating source, it is effective in a same manner asin the above to maintain an atmosphere in a reducing state.

A second aspect is a production method which is characterized in that asolution prepared by dissolving the above described first and secondmetallic elements, oxides thereof or compounds thereof with quartzpowder, while mixing with one another, in pure water, an acidicsolution, an alkaline solution, or an organic solvent is dried toprepare a formed body and, then, the thus-prepared formed body isheat-fused at 1300° C. or higher in a non-acidic atmosphere, to therebyprepare an ingot.

A third aspect is a production method which is characterized in thatpowder prepared by mixing the above described first and second metallicelements, oxides thereof or compounds thereof with quartz powder ispacked in a quartz tube and, then, heat-fused at 1300° C. or higher froman outside face of the tube while allowing an inside of the tube to bein a reduced pressure by sucking the air therein, to thereby prepare aningot.

A fourth aspect is a production method in which a volatile compound gasof the above described first and second metallic elements is diffused ina quartz soot having a hydroxide group and, then, after subjected to aheating treatment in the temperature range of from 200° C. to 1100° C.,heat-fused at 1300° C. or higher in a non-acidic atmosphere, to therebyprepare an ingot.

A fifth aspect is a production method which is characterized in that aquartz soot is dipped in a solution prepared by mix-dissolving theabove-described first and second metallic elements or compounds thereofwhich are dissolvable in pure water, an acidic solution, an alkalinesolution, or an organic solvent, in the pure water, the acidic solution,the alkaline solution, or the organic solvent, dried and, then,heat-fused at a temperature of 1300° C. or higher in a non-acidicatmosphere, to thereby prepare an ingot.

A sixth aspect is a method for producing a quartz glass jig by applyinga solution prepared by mix-dissolving the above described first andsecond metallic elements, oxides thereof or compounds thereof which aredissolvable in pure water, an acidic solution, an alkaline solution, oran organic solvent, in pure water, an acidic solution, an alkalinesolution or an organic solvent on a surface of a previously preparedquartz glass jig and, then, heat-fusing the surface.

Although there is a case in which bubbles each having a size of about1.0 mmφ sometimes remain partially in such doped quartz glass member asproduced in the above-described aspects, the bubbles can becompress-removed by heat-forming the doped quartz glass member at atemperature of 1300° C. or higher under a pressure of 2 kg/cm² or higherin an inert gas atmosphere. The inert gas is favorably an Ar gas and atemperature of the heat forming is favorably 1450° C. or higher.

In such plasma corrosion resistant quartz glass ingot as prepared in theabove-described aspects, contents of the bubbles and the foreign mattersare less than 100 mm² in terms of a projected area per 100 cm³.

As has been described above, according to the present invention, thebubbles and the foreign matters which will cause a problem at the timewhen the glass body is used for a semiconductor industry are not foundin the glass body and, accordingly, the quartz glass which has improvedin the plasma corrosion resistance and has decreased in the etching rateby 50% or more as compared with natural or synthetic quartz glass can beobtained and, also, the metal impurities at such a level as at which aproblem is caused are not found on the silicon wafer all through theetching process.

The present invention is described below by way of examples, but it goeswithout saying that the following examples are given to illustrate thepresent invention and should not be interpreted as limiting it in anyway.

EXAMPLE 1

Powder prepared by mixing 27120 g of quartz particles, 1440 g of Al₂O₃powder, 240 g of Y₂O₃ powder, 240 g of CeO₂ powder, 240 g of Nd₂O₃powder, 240 g of La₂O₃ powder, 240 g of Gd₂O₃ powder and 240 g of Sm₂O₃powder by a ball mill made of quartz glass was fused and dropped at arate of 50 g/min on a target of 300 mmφ×100 mmt rotating at a rate of 1rpm in an oxyhydrogen flame which used a burner having a focusingdistance of 200 mm, to thereby prepare quartz ingot of 200 mmφ×400 mm.The target comprised quartz glass in a thickness of up to 40 mmt fromthe surface and graphite in the subsequent lower portion of from 40 to100 mmt. Gas conditions employed were set as that H₂ was 300 L/min; andO₂ was 100 L/min. An upper ceiling in a heating area was fabricated byaligning alumina sheets each having a strip shape of 40×6×1000 in sizes.During such preparation of the ingot, a side-face heating was performedby a rod-shaped electric heater disposed on a side face of the ingotand, after the flame was distinguished, the ingot was gradually cooleddown to 800° C. consuming 4 hours by gradually weakening an intensity ofthe heating by the heater. The ingot thus prepared was placed in aheating treatment furnace and, then, formed by being held for one hourat 1800° C. under a pressure of 3 kg/cm² in an Ar atmosphere, to therebyprepare a formed body of 500 mmφ×60 mm.

When the bubbles and foreign matters inside the ingot were checked by anoptical visual observation method, amounts of the bubbles and foreignmatters contained were 50 mm² in terms of a projected area per 100 cm³.Further, an internal transmission of visible light was 70%/cm. A samplewas cut out from the glass formed body thus obtained and, then, when aconcentration of the metallic element in the glass body was measured byusing a fluorescent X ray, results as shown in Table 1 were obtained.

Further, a jig having a ring shape of outer diameter: 400 mmφ× innerdiameter: 370 mmφ×200 mmt was cut out from the glass formed body and,then, machined.

A silicon wafer was set in an inner portion of the thus-cut out jig, setin an etching apparatus and, then, while a plasma gas comprising CF₄+O₂(20%) was flown at a rate of 50 sccm in a one-time-use manner, wassubjected to an etching test under conditions of 30 mtorr, 1 kw and 100hours. An etching rate was calculated based on the change in thicknessbefore and after the test, to thereby obtain a result of 30 nm/min.Further, when an analysis of the impurities on the silicon wafer wasexecuted by using the fluorescent X ray, every metallic impurity exceptAl was less than 1×10⁸ atoms/cm², which was not problematic. The resultsare shown in Table 1.

TABLE 1 First M1/M2 metallic Atomic Ingot Etching Metallic elementSecond metallic element number turbidity Ingot rate impurities (wt %)(wt %) ratio point bubble (nm/min) (atoms/cm²) Example 1 Al (4.8) Y(0.8), Nd (0.8), Sm (0.8), 2.6 ◯ ◯ 30 <1 × 10⁸ Ce (0.8), La (0.8), Gd(0.8) Example 2 Al (4.8) Y (0.4), Nd (0.4), Sm (0.4), 5.2 ◯ ◯ 40 <1 ×10⁸ Ce (0.4), La (0.4), Gd (0.4) Example 3 Al (4.8) Y (0.8), Nd (0.8),Sm (0.8) 5.7 ◯ ◯ 40 <1 × 10⁸ Example 4 Al (4.8) Y (0.8) 13.4  ◯ ◯ 50 <1× 10⁸ Comparative — — — ◯ ◯ 120  <1 × 10⁸ Example 1 Comparative Al (4.8)Y (2.4) 4.5 ◯ ◯ 40    1 × 10¹⁵ Example 2 Experimental Al (0.16) Y (0.8),Nd (0.8), Sm (0.8),  0.09 X ◯ 30 <1 × 10⁸ Example 1 Ce (0.8), La (0.8),Gd (0.8) Experimental Al (4.8) Y (0.8), Nd (0.8), Sm (0.8), 2.6 X ◯ 30<1 × 10⁸ Example 2 Ce (0.8), La (0.8), Gd (0.8) Experimental Al (4.8) Y(0.8), Nd (0.8), Sm (0.8), 2.6 ◯ X 30 <1 × 10⁸ Example 3 Ce (0.8), La(0.8), Gd (0.8)

EXAMPLE 2

Same treatments were performed as in Example 1 except for doping 27840 gof quartz particles, 1440 g of Al₂O₃ powder, 120 g of Y₂O₃ powder, 120 gof CeO₂ powder, 120 g of Nd₂O₃ powder, 120 g of La₂O₃ powder, 120 g ofGd₂O₃ powder and 120 g of Sm₂O₃ powder, to thereby obtain results asshown in Table 1. The etching rate was 40 nm/min.

EXAMPLE 3

Same treatments were performed as in Example 1 except for doping 27840 gof quartz particles, 1440 g of A1₂O₃ powder, 240 g of Y₂O₃ powder, 240 gof Nd₂O₃ powder and 240 g of Sm₂O₃ powder, to thereby obtain results asshown in Table 1. The etching rate was 40 nm/min.

EXAMPLE 4

Same treatments were performed as in Example 1 except for doping 28320 gof quartz particles, 1440 g of Al₂O₃ powder and 240 g of Y₂O₃ powder, tothereby obtain results as shown in Table 1. The etching rate was 50nm/min.

EXAMPLE 5

Same treatments were performed as in Example 1 except for using arcplasma as a heating source of the Verneuil method, to thereby obtainsimilar evaluation results to those in Example 1.

EXAMPLE 6

Same treatments were performed as in Example 1 except that a solutionprepared by mix-dissolving quartz particles and a metallic oxide to bedoped in a starting solution was dried and, accordingly, a formed bodywas prepared, to thereby obtain a quartz glass formed body. When asimilar sample to that in Example 1 was prepared and, then, eachevaluation was performed on the thus-prepared sample, similar evaluationresults to those in Example 1 were obtained.

EXAMPLE 7

Same treatments were performed as in Example 1 except that powderprepared by mixing quartz particles and a metallic oxide to be dopes waspacked in a quartz tube and, then, heated from an outer face of the tubeto be fused while allowing the inside of the tube to be in a reducedpressure by sucking the air therein and, accordingly, an ingot wasprepared, to thereby obtain a quartz glass formed body. When a similarsample to that in Example 1 was prepared and, then, each evaluation wasperformed on the thus-prepared sample, similar evaluation results tothose in Example 1 were obtained.

EXAMPLE 8

Same treatments were performed as in Example 1 except that a volatilegaseous compound of a metal to be doped was allowed to be diffused in aquartz soot having a hydroxyl group, subjected to a heating treatment at600° C. and, then, heat-fused and, accordingly, an ingot was prepared,to thereby obtain a quartz glass formed body. When a similar sample tothat in Example 1 was prepared and, then, each evaluation was performedon the thus-prepared sample, similar evaluation results to those inExample 1 were obtained.

EXAMPLE 9

Same treatments were performed as in Example 1 except that a quartz sootbody was dipped in a solution prepared by mix-dissolving a metalliccompound to be doped, dried and, then, heat-fused, to thereby obtain aquartz glass formed body. When a similar sample to that in Example 1 wasprepared and, then, each evaluation was performed on the thus-preparedsample, similar evaluation results to those in Example 1 were obtained.

EXAMPLE 10

A solution prepared by mix-dissolving a metallic compound to be dopedwas applied on a surface of a quartz glass jig and, then, the surfacewas heat-fused, to thereby produce a quartz glass jig. Further, themetallic compound to be doped was same as in Example 1. When a plasmaetching test was performed on the thus-produced quartz glass jig in asame manner as in Example 1, an etching rate was 30 nm/min and metallicimpurities except for Al were not found on a silicon wafer.

EXAMPLES 11 to 14

Same treatments were performed as in Example 1 except for using, as ametallic compound to be doped, B₂O₃ powder, Ga₂O₃ powder, In₂O₃ powderor Tl₂O₃ power in place of Al₂O₃ powder, to thereby obtain a quartzglass formed body. When a similar sample to that in Example 1 wasprepared and, then, each evaluation was performed on the thus-preparedsample, similar evaluation results to those in Example 1 were obtained.

EXAMPLES 15 to 26

Same treatments were performed as in Example 3 except for using, as ametallic compound to be doped, MgO powder, CaO powder, SrO powder, BaOpowder, Sc₂O₃ powder, La₂O₃ powder, CeO₂ powder, Gd₂O₃ powder, Am₂O₃powder, TiO₂ powder, ZrO₂ powder or HfO₂ powder in place of Sm₂O₃powder, to thereby obtain a quartz glass formed body. When a similarsample to that in Example 3 was prepared and, then, each evaluation wasperformed on the thus-prepared sample, similar evaluation results tothose in Example 3 were obtained.

COMPARATIVE EXAMPLE 1

30000 g of quartz particles was filled in a carbon casting mold and,then, subjected to a heating treatment at 1,800° C. for one hour in avacuum atmosphere, to thereby prepare a transparent glass body of 500mmφ×65 mm. Further, when a similar sample to that in Example 1 wasprepared and subjected to a plasma etching test, it was found that anetching rate was 120 nm/min. Other evaluation results than the etchingrate were same as in Example 1.

COMPARATIVE EXAMPLE 2

A sample was prepared in a similar manner to that in Example 3 exceptfor doping 27840 g of quartz particles, 1440 g of Al₂O₃ powder and 720 gof Y₂O₃ powder and, then, subjected to evaluations. The etching rate was45 nm/min. As a result of an analysis of impurities on a silicon wafer,Y was detected as being 1×10¹⁶ atoms/cm², which was problematic.

EXPERIMENTAL EXAMPLE 1

28510 g of quartz particles, 50 g of Al₂O₃ powder, 240 g of Y₂O₃ powder,240 g of CeO₂ powder, 240 g of Nd₂O₃ powder, 240 g of La₂O₃ powder, 240g of Gd₂O₃ powder and 240 g of Sm₂O₃ powder were mixed, fused anddropped at a rate of 50 g/min on a target ingot rotating at a rate of 1rpm in an oxyhydrogen flame, to thereby prepare a quartz ingot of 200mmφ×400 mm. Gas conditions employed were set as that H₂ was 300 L/min;and O₂ was 100 L/min. The thus-prepared ingot was placed in a heatingtreatment furnace and, then, formed to be 500 mmφ×60 mm by being heldfor one hour at 1800° C. under a pressure of 3 kg/cm² in an N₂atmosphere. A multiplicity of turbidity points (foreign matters)remained in the ingot.

EXPERIMENTAL EXAMPLE 2

An ingot was prepared in a similar manner to that in Example 1 exceptfor using an oxyhydrogen flame by the Verneuil method and setting gasconditions in which H₂ was 300 L/min and O₂ was 150 L/min. Amultiplicity of turbidity points (foreign matters) remained in theingot.

EXPERIMENTAL EXAMPLE 3

An ingot prepared in a similar manner to that in Example 1 was set in aheating treatment furnace and, then, formed to be 500 mmφ×60 mm by beingheld for one hour at 1800° C. under a pressure of 1 kg/cm² in an N₂atmosphere. A multiplicity of bubbles of about φ0.5 mm to about φ1.0 mmremained in the ingot.

1. A quartz glass used for a plasma reaction apparatus for producing a semiconductor, said quartz glass containing 0.1 to 20 wt % in total of two or more types of metallic elements, said metallic elements comprising a first metallic element having at least one type of metallic element selected from Group 3B of the periodic table and a second metallic element having at least one type of metallic element selected from the group consisting of Sc, Y, Ti, Zr, Hf, lanthanoids, and actinoids wherein each metallic element of said second metallic elements has a maximum concentration of 2.0 wt % or less.
 2. The quartz glass according to claim 1, wherein said second metallic element has two or more types of metallic elements.
 3. Ihe quartz glass according to claim 1, wherein said second metallic elements has a total concentration of 2.0 wt % or more.
 4. The quartz glass according to claim 1, wherein said first metallic element is Al, and said second metallic element comprises at least one type of metallic element selected from the group consisting of Y, La, Ce, Nd, Sm, and Gd.
 5. The quartz glass according to claim 1, wherein the blend ratio of said first metallic element (M1) and the total of one or two types or more of said second metallic element (M2), (M1)/(M2), in atomic number ratio, is in a range of from 0.1 to20.
 6. The quartz glass according to claim 1, which comprises a total content of bubbles and foreign matter of less than 100 mm² per 100 cm³ area.
 7. A quartz glass containing 0.1 to 20 wt % in total of two or more types of metallic elements, said metallic elements comprising a first metallic element having at least one type of metallic element selected from Group 3B of the periodic table and a second metallic element having at least one type of metallic element selected from the group consisting of Mg, Ca, Sr, Ba Sc, Y, Ti, Zr, Hf, lanthanoids, and actinoids, wherein each metallic element of said second metallic element has a maximum concentration of 2.0 wt % or less, wherein said quartz glass is manufactured by a Verneuil method comprising the steps of supplying a powder raw material prepared by mixing quartz powder with the powders of said first and second metallic elements or the powder of the compound thereof to a burner, and in case of dropping a hot-molten product to produce a quartz glass ingot, heating the surface temperature of said quartz glass ingot to 1800° C. or higher. 